1. Field of the Invention
The present invention relates to a method for controlling longitudinal movement of a motor vehicle; and more particularly, a method for stopping the vehicle.
2. Description of Related Art
A vehicle service brake operates to smoothly stop a motor vehicle, also referred to as a “soft stop”. For example, one method for smooth stopping of a motor vehicle includes reducing the hydraulic pressure generated by a foot force-activated brake system, independently of the driver, in a stopping operation.
Vehicles having automatic transmissions typically include a converter between the engine and the automatic transmission. When the transmission is in the “drive state” and the vehicle is braked by means of the service brake or the parking brake until the vehicle is at a standstill, slip occurs in the converter, resulting in a creep torque wherein if the brake is released, the vehicle starts speeding up until a torque equilibrium has set in. With no brakes at all the vehicle settles at a speed of approximately 5 km/h (maximum creep speed). It therefore follows that the creep torque is greatest when the vehicle is at a standstill, because the torque transferred by the converter is generally a function of the input speed and the output speed at the converter. When the vehicle accelerates, the output speed of the converter increases until the output speed is essentially as great as the input speed, that is it equals the engine speed of the vehicle, and the drive torque transferred by the converter diminishes.
It is difficult to entirely avoid the jolt upon stopping of a motor vehicle as a result of an automated intervention in a brake system of the motor vehicle whereby the jolt is no longer perceived by the occupants of the vehicle. This is due primarily to the fact that the brake pressure applied by the brake system must be extremely precisely metered. If the brake pressure is slightly too high at the stopping instant, i.e., during the transition from kinetic friction to static friction at the vehicle brakes, the jolt upon stopping is still perceptible. If the braking torque generated by the brake pressure is slightly lower, than a creep torque provided by the motor vehicle—for example a vehicle equipped with an automatic transmission, the motor vehicle does not stop.